FIGURE 20 Comto 71. The angle of inclination at a point P on a plane curve is the angle e between the unit tangent vector T and the x-axis (Figure 21). Assume that r(s) is an arc length parametrization, and let 0 = 0(s) be the angle of inclination at r(s). Prove that do K (S ) = ds 13 Hint: Observe that T(s) = (cos 0(s), sin (s)). FIGU T = (cos 0, sin 0) and al 1 Exerci P 5. Let two - X FIGURE 21 The curvature at P is the quantity |de/dsl